Wednesday, June 4, 2014

Exploring the Miracle Piano Teaching System

A few years back, still living at my parent's house; I visited a small dirty yard sale hosted by a previously incarcerated criminal (or so he liked to brag). Oddly enough it was a combination of baby toys and power tools, but with one gem. Probably the best yard-sadly-deal I have ever found is my $5 Miracle Piano!

The sounds that it produces are pretty basic and common to other digital keyboards, but with a few more interesting ones. The keyboard has a "synth" option which sounds pretty cool and a bunch of drum samples, dog barking, ducks quacking and car screeching. Not only that, but it has MIDI input, MIDI output, RCA audio out, headphone out and internal stereo speakers. The last two things to mention are the footpedal input which I have yet to use and the data port connection which connects to wither the NES, Sega Genesis, PC, or whatever other game console/computer it was designed for. All I would need is a special cable and the software, but I can't be happier with the keyboard itself.

I can't necessarily play any instruments, but my goal is to incorporate this keyboard into my modular kit. I hope to modify the audio output to be compatible with the "eurorack" parameters such as 10vpp (+/-5v) audio output, maybe a 0/5v gate or trigger output for when a key is pressed. I started by opening it up and tracing the speaker audio back to the source. I started probing from resistor to capacitor to op amp ... and a few hours later I still saw no end to JUST the left audio! This thing is overly complex it seems, so I took a break since then. I would like to not only take the audio signal itself, but also to mod the MIDI out signal with some sort of MIDI-to-CV converter which I am sure there are many different options for.

In any case, here are some photos to tide people over until I make some real progress:

Above is the board covered in what I assume is a ground plane to reduce noise. The screw terminals connect it to ground. Nothing but a pretty blue shielding.

And here is the bottom of the board. On this side you can see the external connectors, audio outputs and voltage regulation components.

And here is the good stuff. Several proprietary "Software Toolworks" ICs, some sort of microcontroller (maybe) ROM, RAM, and some other unidentified IC.

Above you can see the top right corner which has several op amps. The TDA connects most closely to the RCA outputs and speaker and if I recall correctly, the headphone too. The 5532 IC seems to connect only to one of the audio channels though which confuses me since there is only one 5532.

A closeup of the buttons, some LEDs and the key connectors at the bottom. This also shows one of the post-production modifications at the left. There are several modifications that they made the the final board before sale. MOre shown below.

This is a wide shot of several of the jumper wires that they added before sale, but after production. There seems to be a lot of them... It also shows the larger ICs which need identifying.

Yet more ICs and resistor arrays.

Here is a closeup of the ROM and RAM. It also clearly shows the text on some of the unknown ICs.

Above is the same photo, but with the sticker on the ROM removed. I will dump this ROM as soon as I get the chance and release the binary. Speculating, I bet it is some program and some sound samples. If we can figure out what is program and what is a sample, then the samples should be able to be replaced which could prove very interesting!